Ink jet single-nozzle printing head

ABSTRACT

In a ink jet printing head, all essential elements are made integral with a monolithic part (2) acting as a base. Furthermore, the modulation body (10) cooperates with adjusting means (screw 84 and oblong holes 85) according to two angles (α) and (β), situated in two perpendicular planes. The charge (71), charge-control (72l ) and deflexion (73, 74) electrodes are integral with a block (70). The electric isolation is provided particularly by means of a groove (89) and a web (90), thereby preventing any arc formation. The inventon can be applied to any ink jet printer.

The invention relates to a single nozzle ink jet printing head.

The ink jet printing technique includes forming a continuous jet ofcalibrated drops, supplied by a modulation system then inelectrostatically charging these drops by means of charge electrodes, soas to deflect each drop by means of an electric field so that if thesupport on which it is desired to write and the writing device aremoving relatively to each other, the formation of a printing matrix isobtained.

In an ink jet printer, the above mentioned function, namely thefragmentation of the jet into calibrated drops, the electrostatic chargethereof and deflection thereof are obtained by means of a device calledprinting head in the rest of the description.

The role of this head is fundamental for the correct operation of an inkjet printer. In particular the path of the drops ejected at the level ofthe injection nozzle must be perfectly defined with respect to thecharge electrodes the deflection plates and the support which receivesthe impression. The printing head complying with these criteria must inaddition be compact, require no adjustment during operation and allowsimple and reliable adjustments to be made previous to starting up.Finally, this head must have a great facility of access for maintenancepurposes.

A printing head corresponding to these criteria has been described in aFrench patent application 82 03975 filed on the 7th Mar. 1983 by theapplicant. In this printing head, the means for breaking the jet andejecting the drops are fixed to the body of the cap and the charging anddeflecting means are fixed to the lid of said cap.

In the present application, on the other hand, all these essentialelements of the printing head are fixed to one and the same monolithicpiece, this architecture contributing to reducing the space required bythe assembly without adversely affecting the adjustment facilities, northe isolating conditions, particularly of the deflection electrodes.

Another object of the invention is to described a support block for theintegrated charge control electrodes and deflection plates.

Another object relates to a safety device limiting the current in thecircuit feeding the deflection means.

The invention also relates more precisely to a single nozzle ink jetprinting head of the type having an ink supply circuit, a signalamplifier, an ink recovery detector, means for breaking the jet andejecting the drops, means for charging and deflecting the drops;characterized in that the whole of these means is fixed to a monolithicpiece serving, on the one hand, as base for the means and, on the otherhand, as case for cooperating with a lid for forming the covering cap ofthe head.

The invention will be better understood from the following explanationsand accompanying Figures in which:

FIG. 1 illustrates an important part of a printing head including theessential functional elements such as the drop formation and injectionmeans, the means for charging the drops and the deflection means.

FIGS. 2 and 3 illustrate schematically the main elements described withreference to FIG. 1.

FIG. 4 is an exploded view of the components forming a printing head inaccordance with the invention.

For the sake of clarity, the same elements bear the same references inall the Figures.

As shown in FIG. 1, completed by FIGS. 2 and 3 to which the rest of thedescription simultaneously refers, a printing head 1 according to theinvention is formed of a monolithic piece 2. This piece 2 fulfills twofunctions: on the one hand it plays the role of cap body, and on theother it serves as base for all the means providing the essentialfunctions of the head: namely, particularly the means for forming andejecting the drops, charging them and deflecting them. A lid closes thecase but it has no other function, contrary to what happens in the caseof the printing head described in the above mentioned patent, no otherfunction than that of closing the case, while allowing the combinationof the above mentioned means to be examined when it is open.

These latter means are all shown in FIG. 1, where only the complementaryenvironment is missing which is not directly in relation with theinvention. In the top part (A) we find the inlet of the ink supplycircuit 100 fixed to head 1 by means of a connecting nut 101 partiallyshown). We also find the signal amplifier 40. This latter may beenclosed in a cavity (not shown) provided for this purpose in case 2.

Finally, a detector 14 for the recovery of ink recovered at the level ofgutter 7 via duct 77 is also housed therein. This detector 14 is fixedto the monolithic piece 2 by fixing means 45 and comprises integrally aresistance R which fulfills a current limiting function as will beexplained further on.

The central part M also includes the modulation means causing break upof the jet and the means for ejecting the drops thus created.

The modulation body 10 is carried by a support 13, made from aninsulating material which is fixed to the monolithic piece 2 by a set ofscrews 120. Inside this modulation body is introduced the combination ofthe piezoelectric transducer 11 associated with its resonator 12 at theend of which is placed the plate 20 supporting the nozzle 21. This plate20 is fixed to support 13 for example by means of a screw 95 mountedperpendicularily.

An O seal 210 is provided at the top end of resonator 12. In combinationwith a packing 110 it provides sealing at this level. A second O seal211 is also provided at the low part of the modulation body and itprovides sealing between this body 10 and the plate 20 holding nozzle21. The modulation body 10 of the invention may be oriented in twoperpendicular planes through two angles (α) and (β). In fact, it mayrotate about a first positioning and centering pin 80 giving it thedegree of freedom through (β) and about a second pin (16) giving it thedegree of freedom through (α).

When the correct positioning of the modulation body and so of the jet isobtained, screws 85 cooperating with oblong holes 84 lock body 10 in thetwo planes.

Connections 56 connect the ink circuit to the modulation body.

The low part D concerns the combination of the charging electrodes andthe members deflecting the ink drops. More precisely and according toanother important characteristic of the invention, it is a sub assemblyalso monolithic formed of a support block 70 on which are mounted thecharge 71 and charge control 72 electrode as well as the left 73 andright 74 deflection plates.

According to another important characteristic of the invention, thiselectrode support block 70 is made from an isulating material whosedielectric characteristics and thicknesses ensure, between themonolithic base 2 and said electrodes, an insulating level compatiblewith the voltages used at this level. In addition, so as to avoid arcformation, an insulating groove 89 as well as a web 90 providing averitable insulating wall is provided on the side of the deflectionelectrode brought to a very high voltage.

The charge control electrode 72 is for example of the type described inthe patent application No. 83 07549 filed on the 29th Apr. 1983 by theapplicant. In this case it is formed of a cylindrical assembly 60 madefrom a conducting material having a bore in which is introduced a secondtube 62 made from an insulating material. This latter is introduced intocylinder 60 so that its external surface is in perfect contact with theinternal surface of cylinder 60 over a given length less than that ofcylinder 60. This second tube 62 forms a sleeve inside which isintroduced a solid cylinder 63 made from a conducting material. In thisassembly a slit 65 is formed through which the ink drops transit, shownwith broken lines. According to a characteristic of the presentinvention, two light emitting diodes 86 and 87 are positionedrespectively, the first one within the charge electrode 71 and thesecond at the output of the charge control electrode 72. Diode 86 allowsthe quality of the drop formation to be checked visibly and diode 87allows the speed of these drops to be measured visually.

This electrode support block 70 also supports the left deflection plates73 and 74 which are fixed for example by means of screws 58. However,according to an important characteristic of the invention, taking intoaccount the geometry of this support block 70 and its structure,deflection electrodes may be deposited on the internal wall of thissupport in the form of a layer of conducting material which then playsthe role of the above described deflection plate 73 and 74. According tothe invention, one of the deflection plates (73) or layer is brought toa high potential (of the order of 800 volts for example) whereas thesecond deflection plate 74 (or layer) is kept at zero potential.

As was mentioned above, considering the electrical requirements, theinsulation between the support blocks 70 and the monolithic base 2, aswell as between this block 70 and the charge electrode 71 must beefficiently provided. To fulfill this function, on the one hand, thethickness of the support block 70 itself made from an insulatingmaterial is optimized and, on the other hand, an insulating groove 89and a wall 90 are provided for this purpose.

An adjustment means 57 sliding laterally on two pins 810 ensures thetranslational positioning (τ) of the support block 70 and allows the twodeflection plates or layers to be perfectly positioned with respect tothe jet of drops.

FIG. 4, which is an exploded view of a printing head in accordance withthe invention, recapitulates the assembly of components forming it andallows mounting thereof to be visualized.

We find again then the monolithic piece 2 whose wall 180 serves as basefor the assembly of the elements forming head 1. A connection 181 andits nut 101 fix the external ink circuit to the upper bottom 182. Onthis wall 180, a box (cavity) not shown is provided for enclosing andshielding the signal amplifier 40. At this level is also housed the inkrecovery detector 14.

According to an important characteristic of the invention, as hasalready been mentioned, this detector 14 is made from an insulatingmaterial and comprises a resistor R integrated in this insulator. Thisresistance is mounted in series in the circuit THT of the deflectionplate 73 brought to the potential of 8000 volts so that in the case ofbreakdown of this latter, this resistor R plays the role of currentlimiter.

The coaxial cable 26 like the circuit THT 27 are connectedconventionally by means of tags 28.

According to an important characteristic of the invention, as hasalready been mentioned and which is particularly illustrated in FIG. 4,the modulation body 10 with the nozzle carrying base 20 is orientatablethrough two angles (α) and (β); thus the ink jet may be perfectlycentered by adjusting these two degrees of freedom.

In this FIG. 4 are also clearly shown the charging and charge controlelectrodes, as well as the deflection electrodes (or layers) whoseinsulation is provided by means of the above described insulating grooveand wall.

The lower bottom 70 of the monolithic base 2 has an orifice 97 throughwhich transit the deflected drops before reaching the surface duringmarking (not shown in the Figure). The recovery gutter 7 is fixed by aflange 107. Finally, a lid 130 is fixed to the monolithic base 2 bymeans of clips 131 thus forming an external cover protecting theprinting head 1. Such a printing head is compact, easy to adjust andfinds its application in ink jet printers with a single nozzle head.

We claim:
 1. A single nozzle ink jet printing head (1) of the typeincluding a supply circuit (100), means for breaking up the jet andejecting the drops, means for charging and deflecting these latter;characterized in that a signal amplifier (40), a modulation body (10)orientable through two angles (α) and (β) in two perpendicular planes, asupport block (70) in which are integrated the charge (71) and chargecontrol (72) electrodes and the deflection electrodes (73) and (74) aremounted in a monolithic piece (2), this latter serving both forshielding the amplifier (40) and for supporting the modulation body (10)and the support block (70).
 2. Printing head according to claim 1,characterized in that means for adjustment along (tr) allow the supportblock (70) supporting the charge and drop deflection electrodes to bepositioned, by translation along (tr), in the axis of the jet. 3.Printing head according to claim 1, characterized in that a groove (89)and a web (90) provide the insulation of the charged deflection plate(73).
 4. Printing head according to claim 1, characterized in that twolight emitting diodes (86) and (87) are integrated in the support block(70), the first at the level of the charge electrode (71) for visuallychecking the formation of the drops, the other at the level of thecharge control electrode (72) for visually checking the speed of thesedrops.
 5. Printing head according to claim 1, characterized in that twoelectrodes (73) and (74) are formed by two metal layers deposited on theinternal wall of the support block (70).
 6. Printing head according toclaim 1, characterized in that one of the deflection electrodes (73) isbrought to a very high potential, the second electrode (74) being keptat zero potential.
 7. Printing head according to claim 1, characterizedin that it includes a charge control electrode integrated in a blocksupporting the charge electrode (71) and the deflection plates (73) and(74).
 8. Printing head according to claim 1, characterized in that anink detector placed in the ink recovery circuit (77) connected to thegutter (7) has a resistor (R) mounted in series in the circuit placingthe deflection electrodes (73) and (74) under tension.